Field of the Invention
The present invention relates to an eyepiece lens, an observation apparatus including the eyepiece lens and an image pickup apparatus including the eyepiece lens, which are suitable for observing an image displayed on an image displaying surface of an image displaying element through, for example, an electronic view finder to be used for a video camera, a still camera, or a broadcasting camera.
Description of the Related Art
Hitherto, in an electronic view finder to be used for an image pickup apparatus such as a video camera or a still camera, an eyepiece lens for observing an image displayed on a liquid crystal screen or the like in an enlarged manner is used. In order to increase visibility of an image displaying surface in the electronic view finder, for example, it is necessary to increase the size of the image displaying surface of the liquid crystal screen, or the like, or to increase a magnification factor for observation through use of an eyepiece lens having a long focal length.
In general, when an eyepiece lens having a long focal length is used, a movement amount of a lens unit for diopter adjustment increases at the time of diopter adjustment. As a result, the size of a finder optical system increases. Therefore, hitherto, there has been known an eyepiece lens configured such that a part of the lens units forming the eyepiece lens is moved, to thereby adjust the diopter with a small movement amount and thus achieve a size reduction of the finder optical system.
In Japanese Patent Application Laid-Open No. 2004-109961, there is disclosed an eyepiece lens consisting of, in order from an image displaying surface side to an observation side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power. Further, the first lens unit consists of a single negative lens, and the second lens unit consists of a cemented lens formed by cementing together a positive lens and a negative lens. During diopter adjustment, the first lens unit or the second lens unit is configured to move. In Japanese Patent Application Laid-Open No. 2000-98266, there is disclosed an eyepiece lens consisting of, in order from an image displaying surface side to an observation side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. During diopter adjustment, the second lens unit is configured to move.
When the diopter is adjusted in the eyepiece lens to be used for the observation apparatus, it is important that the diopter be adjusted over a wide range based on the movement of the lens unit for diopter adjustment and that the eyepiece lens have satisfactory optical characteristics over a wide diopter adjustment range. In addition, for example, it is important that the lens unit for diopter adjustment have a small size and weight so that the diopter may be adjusted quickly and easily.
In order to obtain an eyepiece lens satisfying such requirements, it is important to appropriately configure the lens structure of the eyepiece lens, the lens structure of the lens unit for diopter adjustment, and the like. In addition, when an image displaying surface having a large size is used, it is important to appropriately set, for example, a ratio of the refractive power of each lens unit forming the eyepiece lens to the size of the image displaying surface, in particular, a ratio of the refractive power of the lens unit for diopter adjustment to the size of the image displaying surface.
In the eyepiece lens disclosed in Japanese Patent Application Laid-Open No. 2004-109961, the shape of the negative lens on the observation side is not appropriate when this eyepiece lens is applied to a finder optical system using an image displaying surface having a large size. Therefore, when the second lens unit is moved during diopter adjustment, a principal point of the second lens unit cannot be moved sufficiently toward the image displaying surface side, and hence diopter adjustment to a negative diopter is often limited. In the eyepiece lens disclosed in Japanese Patent Application Laid-Open No. 2000-98266, a lateral chromatic aberration varies greatly during diopter adjustment, and hence it often becomes difficult to obtain high optical characteristics over a wide diopter adjustment range.